We have cloned a tetrodotoxin-resistant (TTX-R) voltage-gated sodium channel ex subunit from a mouse cDNA library and designated it as NaT, It encodes 1765 amino acid residues and is virtually identical to that of Scn11a, which has been reported recently, except for 40 nt and 14 aa substitutions. The amino acid identity of NaT/Scn11a with rat NaN/SNS2 is 88%, NaT/Scn11a was mapped to mouse chromosome 9F3-F4 by fluorescence in situ hybridization (FISH), While rat NaN/ SNS2 has been reported to be expressed specifically in the peripheral sensory neurons, NaT/Scn11a is expressed not only in the peripheral sensory neurons but also in the spinal cord, uterus, testis, ovary, placenta, and small intestine. NaT is detectable in mouse embryos 15 days postcoitus (p.c.), around the phase of organogenesis and gonadal differentiation. These findings demonstrate a unique distribution of NaT/ Scn11a and suggest some of its roles in the above-mentioned processes.